Philosopher and ethicist David Pearce points to the possibilities:
Pain and pain-thresholds are modulated by a number of different genes. Let's focus on just one of them here: SCN9A. … [I]f we're ethically serious about reducing the burden of suffering in the world, we could use preimplantation genetic diagnosis (PGD) to choose benign "low pain" variants of the SCN9A gene for our future children. Prudence dictates that we shouldn't (yet) abolish the capacity for phenomenal pain altogether. But we can still ensure that pain has a negligible impact on our children's quality of life by selecting "low pain" alleles for their genomes.